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<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="spirit.advanced.customize.iterate.container_iterator"></a><a class="link" href="container_iterator.html" title="Determine the Type of the Iterator of a Container">Determine
          the Type of the Iterator of a Container</a>
</h5></div></div></div>
<h6>
<a name="spirit.advanced.customize.iterate.container_iterator.h0"></a>
            <span class="phrase"><a name="spirit.advanced.customize.iterate.container_iterator.container_iterator"></a></span><a class="link" href="container_iterator.html#spirit.advanced.customize.iterate.container_iterator.container_iterator">container_iterator</a>
          </h6>
<p>
            The template <code class="computeroutput"><span class="identifier">container_iterator</span></code>
            is a template meta-function used as an attribute customization point.
            It is invoked by the <span class="emphasis"><em>Karma</em></span> repetitive generators
            (such as <a class="link" href="../../../karma/reference/operator/list.html" title="List Generator (a % b)">List (<code class="computeroutput"><span class="special">%</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/kleene.html" title="Kleene Star Generator (*a)">Kleene
            (unary <code class="computeroutput"><span class="special">*</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/plus.html" title="Plus Generator (+a)">Plus (unary <code class="computeroutput"><span class="special">+</span></code>)</a>, and <a class="link" href="../../../karma/reference/directive/repeat.html" title="Repetition Generator Directive (repeat[])">Repeat</a>)
            in order to determine the type of the iterator to use to iterate over
            the items to be exposed as the elements of a container.
          </p>
<h6>
<a name="spirit.advanced.customize.iterate.container_iterator.h1"></a>
            <span class="phrase"><a name="spirit.advanced.customize.iterate.container_iterator.module_headers"></a></span><a class="link" href="container_iterator.html#spirit.advanced.customize.iterate.container_iterator.module_headers">Module
            Headers</a>
          </h6>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">home</span><span class="special">/</span><span class="identifier">support</span><span class="special">/</span><span class="identifier">container</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<p>
            Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>.
          </p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
              This header file does not need to be included directly by any user
              program as it is normally included by other Spirit header files relying
              on its content.
            </p></td></tr>
</table></div>
<h6>
<a name="spirit.advanced.customize.iterate.container_iterator.h2"></a>
            <span class="phrase"><a name="spirit.advanced.customize.iterate.container_iterator.namespace"></a></span><a class="link" href="container_iterator.html#spirit.advanced.customize.iterate.container_iterator.namespace">Namespace</a>
          </h6>
<div class="informaltable"><table class="table">
<colgroup><col></colgroup>
<thead><tr><th>
                    <p>
                      Name
                    </p>
                  </th></tr></thead>
<tbody><tr><td>
                    <p>
                      <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">traits</span></code>
                    </p>
                  </td></tr></tbody>
</table></div>
<h6>
<a name="spirit.advanced.customize.iterate.container_iterator.h3"></a>
            <span class="phrase"><a name="spirit.advanced.customize.iterate.container_iterator.synopsis"></a></span><a class="link" href="container_iterator.html#spirit.advanced.customize.iterate.container_iterator.synopsis">Synopsis</a>
          </h6>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Container</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Enable</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">container_iterator</span>
<span class="special">{</span>
    <span class="keyword">typedef</span> <span class="special">&lt;</span><span class="identifier">unspecified</span><span class="special">&gt;</span> <span class="identifier">type</span><span class="special">;</span>
<span class="special">};</span>
</pre>
<h6>
<a name="spirit.advanced.customize.iterate.container_iterator.h4"></a>
            <span class="phrase"><a name="spirit.advanced.customize.iterate.container_iterator.template_parameters"></a></span><a class="link" href="container_iterator.html#spirit.advanced.customize.iterate.container_iterator.template_parameters">Template
            parameters</a>
          </h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Parameter
                    </p>
                  </th>
<th>
                    <p>
                      Description
                    </p>
                  </th>
<th>
                    <p>
                      Default
                    </p>
                  </th>
</tr></thead>
<tbody>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">Container</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      The type, <code class="computeroutput"><span class="identifier">Container</span></code>
                      for which the iterator type has to be returned
                    </p>
                  </td>
<td>
                    <p>
                      none
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">Enable</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      Helper template parameter usable to selectively enable or disable
                      certain specializations of <code class="computeroutput"><span class="identifier">container_iterator</span></code>
                      utilizing SFINAE (i.e. <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">enable_if</span></code>
                      or <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">disable_if</span></code>).
                    </p>
                  </td>
<td>
                    <p>
                      <code class="computeroutput"><span class="keyword">void</span></code>
                    </p>
                  </td>
</tr>
</tbody>
</table></div>
<div class="variablelist">
<p class="title"><b>Notation</b></p>
<dl class="variablelist">
<dt><span class="term"><code class="computeroutput"><span class="identifier">C</span></code></span></dt>
<dd><p>
                  A container type the iterator type needs to be evaluated for.
                </p></dd>
</dl>
</div>
<h6>
<a name="spirit.advanced.customize.iterate.container_iterator.h5"></a>
            <span class="phrase"><a name="spirit.advanced.customize.iterate.container_iterator.expression_semantics"></a></span><a class="link" href="container_iterator.html#spirit.advanced.customize.iterate.container_iterator.expression_semantics">Expression
            Semantics</a>
          </h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Expression
                    </p>
                  </th>
<th>
                    <p>
                      Semantics
                    </p>
                  </th>
</tr></thead>
<tbody><tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">container_iterator</span><span class="special">&lt;</span><span class="identifier">C</span><span class="special">&gt;::</span><span class="identifier">type</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      Result of the metafunction that evaluates the type to be used
                      as the iterator for accessing all elements of a container,
                      <code class="computeroutput"><span class="identifier">C</span></code>.
                    </p>
                  </td>
</tr></tbody>
</table></div>
<p>
            The returned type conceptually needs to be equivalent to a standard forward
            iterator. But it does not have to expose the standardized interface.
            If this customization point is implemented for a certain container type,
            all related customization points need to be implemented as well (see
            <a class="link" href="container_iterator.html#spirit.advanced.customize.iterate.container_iterator.related_attribute_customization_points">Related
            Attribute Customization Points</a> below). This encapsulates the specific
            iterator interface required for a given type. The minimal requirements
            for a type to be exposed as an iterator in this context are:
          </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
                it needs to be comparable for equality (see <a class="link" href="compare_iterators.html" title="Compare two Iterator pointing into a Container Attribute for Equality"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">compare_iterators</span></code></a>),
              </li>
<li class="listitem">
                it needs to be incrementable (see <a class="link" href="next_iterator.html" title="Increment the Iterator pointing into a Container Attribute"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">next_iterator</span></code></a>),
              </li>
<li class="listitem">
                it needs to be dereferencible (see <a class="link" href="deref_iterator.html" title="Dereference the Iterator pointing into a Container Attribute"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">deref_iterator</span></code></a>).
              </li>
</ul></div>
<h6>
<a name="spirit.advanced.customize.iterate.container_iterator.h6"></a>
            <span class="phrase"><a name="spirit.advanced.customize.iterate.container_iterator.predefined_specializations"></a></span><a class="link" href="container_iterator.html#spirit.advanced.customize.iterate.container_iterator.predefined_specializations">Predefined
            Specializations</a>
          </h6>
<p>
            <a href="http://boost-spirit.com" target="_top">Spirit</a> predefines specializations
            of this customization point for several types. The following table lists
            those types together with the types returned by the embedded typedef
            <code class="computeroutput"><span class="identifier">type</span></code>:
          </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Template Parameters
                    </p>
                  </th>
<th>
                    <p>
                      Semantics
                    </p>
                  </th>
</tr></thead>
<tbody>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">C</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      Returns <code class="computeroutput"><span class="identifier">C</span><span class="special">::</span><span class="identifier">iterator</span></code>.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">C</span> <span class="keyword">const</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      Returns <code class="computeroutput"><span class="identifier">C</span><span class="special">::</span><span class="identifier">const_iterator</span></code>.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">unused_type</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      Returns <code class="computeroutput"><span class="identifier">unused_type</span></code><code class="computeroutput">
                      <span class="keyword">const</span><span class="special">*</span></code>.
                    </p>
                  </td>
</tr>
</tbody>
</table></div>
<h6>
<a name="spirit.advanced.customize.iterate.container_iterator.h7"></a>
            <span class="phrase"><a name="spirit.advanced.customize.iterate.container_iterator.when_to_implement"></a></span><a class="link" href="container_iterator.html#spirit.advanced.customize.iterate.container_iterator.when_to_implement">When
            to implement</a>
          </h6>
<p>
            The customization point <code class="computeroutput"><span class="identifier">container_iterator</span></code>
            needs to be implemented for a specific type whenever this type is to
            be used as an attribute in place of a STL container. It is applicable
            for generators (<span class="emphasis"><em>Spirit.Karma</em></span>) only. As a rule of
            thumb: it has to be implemented whenever a certain type is to be passed
            as an attribute to a generator normally exposing a STL container, <code class="computeroutput"><span class="identifier">C</span></code> and if the type does not expose the
            interface of a STL container (i.e. <code class="computeroutput"><span class="identifier">is_container</span><span class="special">&lt;</span><span class="identifier">C</span><span class="special">&gt;::</span><span class="identifier">type</span></code>
            would normally return <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">false_</span></code>).
          </p>
<h6>
<a name="spirit.advanced.customize.iterate.container_iterator.h8"></a>
            <span class="phrase"><a name="spirit.advanced.customize.iterate.container_iterator.related_attribute_customization_points"></a></span><a class="link" href="container_iterator.html#spirit.advanced.customize.iterate.container_iterator.related_attribute_customization_points">Related
            Attribute Customization Points</a>
          </h6>
<p>
            If this customization point is implemented, the following other customization
            points might need to be implemented as well.
          </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Name
                    </p>
                  </th>
<th>
                    <p>
                      When to implement
                    </p>
                  </th>
</tr></thead>
<tbody>
<tr>
<td>
                    <p>
                      <a class="link" href="../is_container.html" title="Determine if a Type Should be Treated as a Container (Qi and Karma)"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">is_container</span></code></a>
                    </p>
                  </td>
<td>
                    <p>
                      Needs to be implemented whenever a type is to be used as a
                      container attribute in <span class="emphasis"><em>Karma</em></span>.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <a class="link" href="container_iterator.html" title="Determine the Type of the Iterator of a Container"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">container_iterator</span></code></a>
                    </p>
                  </td>
<td>
                    <p>
                      Karma: <a class="link" href="../../../karma/reference/operator/list.html" title="List Generator (a % b)">List
                      (<code class="computeroutput"><span class="special">%</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/kleene.html" title="Kleene Star Generator (*a)">Kleene (unary
                      <code class="computeroutput"><span class="special">*</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/plus.html" title="Plus Generator (+a)">Plus (unary
                      <code class="computeroutput"><span class="special">+</span></code>)</a>, <a class="link" href="../../../karma/reference/directive/repeat.html" title="Repetition Generator Directive (repeat[])">Repeat</a>.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <a class="link" href="begin_container.html" title="Get the Iterator pointing to the Begin of a Container Attribute"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">begin_container</span></code></a>
                    </p>
                  </td>
<td>
                    <p>
                      Karma: <a class="link" href="../../../karma/reference/operator/list.html" title="List Generator (a % b)">List
                      (<code class="computeroutput"><span class="special">%</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/kleene.html" title="Kleene Star Generator (*a)">Kleene (unary
                      <code class="computeroutput"><span class="special">*</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/plus.html" title="Plus Generator (+a)">Plus (unary
                      <code class="computeroutput"><span class="special">+</span></code>)</a>, <a class="link" href="../../../karma/reference/directive/repeat.html" title="Repetition Generator Directive (repeat[])">Repeat</a>.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <a class="link" href="end_container.html" title="Get the Iterator pointing to the End of a Container Attribute"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">end_container</span></code></a>
                    </p>
                  </td>
<td>
                    <p>
                      Karma: <a class="link" href="../../../karma/reference/operator/list.html" title="List Generator (a % b)">List
                      (<code class="computeroutput"><span class="special">%</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/kleene.html" title="Kleene Star Generator (*a)">Kleene (unary
                      <code class="computeroutput"><span class="special">*</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/plus.html" title="Plus Generator (+a)">Plus (unary
                      <code class="computeroutput"><span class="special">+</span></code>)</a>, <a class="link" href="../../../karma/reference/directive/repeat.html" title="Repetition Generator Directive (repeat[])">Repeat</a>.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <a class="link" href="deref_iterator.html" title="Dereference the Iterator pointing into a Container Attribute"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">deref_iterator</span></code></a>
                    </p>
                  </td>
<td>
                    <p>
                      Karma: <a class="link" href="../../../karma/reference/operator/list.html" title="List Generator (a % b)">List
                      (<code class="computeroutput"><span class="special">%</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/kleene.html" title="Kleene Star Generator (*a)">Kleene (unary
                      <code class="computeroutput"><span class="special">*</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/plus.html" title="Plus Generator (+a)">Plus (unary
                      <code class="computeroutput"><span class="special">+</span></code>)</a>, <a class="link" href="../../../karma/reference/directive/repeat.html" title="Repetition Generator Directive (repeat[])">Repeat</a>.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <a class="link" href="next_iterator.html" title="Increment the Iterator pointing into a Container Attribute"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">next_iterator</span></code></a>
                    </p>
                  </td>
<td>
                    <p>
                      Karma: <a class="link" href="../../../karma/reference/operator/list.html" title="List Generator (a % b)">List
                      (<code class="computeroutput"><span class="special">%</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/kleene.html" title="Kleene Star Generator (*a)">Kleene (unary
                      <code class="computeroutput"><span class="special">*</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/plus.html" title="Plus Generator (+a)">Plus (unary
                      <code class="computeroutput"><span class="special">+</span></code>)</a>, <a class="link" href="../../../karma/reference/directive/repeat.html" title="Repetition Generator Directive (repeat[])">Repeat</a>.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <a class="link" href="compare_iterators.html" title="Compare two Iterator pointing into a Container Attribute for Equality"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">compare_iterators</span></code></a>
                    </p>
                  </td>
<td>
                    <p>
                      Karma: <a class="link" href="../../../karma/reference/operator/list.html" title="List Generator (a % b)">List
                      (<code class="computeroutput"><span class="special">%</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/kleene.html" title="Kleene Star Generator (*a)">Kleene (unary
                      <code class="computeroutput"><span class="special">*</span></code>)</a>, <a class="link" href="../../../karma/reference/operator/plus.html" title="Plus Generator (+a)">Plus (unary
                      <code class="computeroutput"><span class="special">+</span></code>)</a>, <a class="link" href="../../../karma/reference/directive/repeat.html" title="Repetition Generator Directive (repeat[])">Repeat</a>.
                    </p>
                  </td>
</tr>
</tbody>
</table></div>
<h6>
<a name="spirit.advanced.customize.iterate.container_iterator.h9"></a>
            <span class="phrase"><a name="spirit.advanced.customize.iterate.container_iterator.example"></a></span><a class="link" href="container_iterator.html#spirit.advanced.customize.iterate.container_iterator.example">Example</a>
          </h6>
<p>
            Here are the header files needed to make the example code below compile:
          </p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">karma</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">vector</span><span class="special">&gt;</span>
</pre>
<p>
          </p>
<p>
            The example (for the full source code please see here: <a href="../../../../../../example/karma/customize_embedded_container.cpp" target="_top">customize_embedded_container.cpp</a>)
            uses the data structure
          </p>
<p>
</p>
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">client</span>
<span class="special">{</span>
    <span class="keyword">struct</span> <span class="identifier">embedded_container</span>
    <span class="special">{</span>
        <span class="comment">// expose the iterator of the embedded vector as our iterator</span>
        <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;::</span><span class="identifier">const_iterator</span> <span class="identifier">iterator</span><span class="special">;</span>

        <span class="comment">// expose the type of the held data elements as our type</span>
        <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;::</span><span class="identifier">value_type</span> <span class="identifier">type</span><span class="special">;</span>

        <span class="comment">// this is the vector holding the actual elements we need to generate </span>
        <span class="comment">// output from</span>
        <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">data</span><span class="special">;</span>
    <span class="special">};</span>
<span class="special">}</span>
</pre>
<p>
          </p>
<p>
            as a direct container attribute to the <a class="link" href="../../../karma/reference/operator/list.html" title="List Generator (a % b)">List
            (<code class="computeroutput"><span class="special">%</span></code>)</a> generator. In
            order to make this data structure compatible we need to specialize a
            couple of attribute customization points: <a class="link" href="../is_container.html" title="Determine if a Type Should be Treated as a Container (Qi and Karma)"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">is_container</span></code></a>, <a class="link" href="container_iterator.html" title="Determine the Type of the Iterator of a Container"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">container_iterator</span></code></a>, <a class="link" href="begin_container.html" title="Get the Iterator pointing to the Begin of a Container Attribute"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">begin_container</span></code></a>, and <a class="link" href="end_container.html" title="Get the Iterator pointing to the End of a Container Attribute"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">end_container</span></code></a>. As you can see
            the specializations simply expose the embedded <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span></code> as the container to use. We don't
            need to specialize the customization points related to iterators (<a class="link" href="deref_iterator.html" title="Dereference the Iterator pointing into a Container Attribute"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">deref_iterator</span></code></a>, <a class="link" href="next_iterator.html" title="Increment the Iterator pointing into a Container Attribute"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">next_iterator</span></code></a>, and <a class="link" href="compare_iterators.html" title="Compare two Iterator pointing into a Container Attribute for Equality"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">compare_iterators</span></code></a>) as we expose
            a standard iterator and the default implementation of these customizations
            handles standard iterators out of the box.
          </p>
<p>
</p>
<pre class="programlisting"><span class="comment">// All specializations of attribute customization points have to be placed into</span>
<span class="comment">// the namespace boost::spirit::traits.</span>
<span class="comment">//</span>
<span class="comment">// Note that all templates below are specialized using the 'const' type.</span>
<span class="comment">// This is necessary as all attributes in Karma are 'const'.</span>
<span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">spirit</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">traits</span>
<span class="special">{</span>
    <span class="comment">// The specialization of the template 'is_container&lt;&gt;' will tell the </span>
    <span class="comment">// library to treat the type 'client::embedded_container' as a </span>
    <span class="comment">// container holding the items to generate output from.</span>
    <span class="keyword">template</span> <span class="special">&lt;&gt;</span>
    <span class="keyword">struct</span> <span class="identifier">is_container</span><span class="special">&lt;</span><span class="identifier">client</span><span class="special">::</span><span class="identifier">embedded_container</span> <span class="keyword">const</span><span class="special">&gt;</span>
      <span class="special">:</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">true_</span>
    <span class="special">{};</span>

    <span class="comment">// The specialization of the template 'container_iterator&lt;&gt;' will be</span>
    <span class="comment">// invoked by the library to evaluate the iterator type to be used</span>
    <span class="comment">// for iterating the data elements in the container. We simply return</span>
    <span class="comment">// the type of the iterator exposed by the embedded 'std::vector&lt;int&gt;'.</span>
    <span class="keyword">template</span> <span class="special">&lt;&gt;</span>
    <span class="keyword">struct</span> <span class="identifier">container_iterator</span><span class="special">&lt;</span><span class="identifier">client</span><span class="special">::</span><span class="identifier">embedded_container</span> <span class="keyword">const</span><span class="special">&gt;</span>
    <span class="special">{</span>
        <span class="keyword">typedef</span> <span class="identifier">client</span><span class="special">::</span><span class="identifier">embedded_container</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">type</span><span class="special">;</span>
    <span class="special">};</span>

    <span class="comment">// The specialization of the templates 'begin_container&lt;&gt;' and </span>
    <span class="comment">// 'end_container&lt;&gt;' below will be used by the library to get the iterators </span>
    <span class="comment">// pointing to the begin and the end of the data to generate output from. </span>
    <span class="comment">// These specializations simply return the 'begin' and 'end' iterators as </span>
    <span class="comment">// exposed by the embedded 'std::vector&lt;int&gt;'.</span>
    <span class="comment">//</span>
    <span class="comment">// The passed argument refers to the attribute instance passed to the list </span>
    <span class="comment">// generator.</span>
    <span class="keyword">template</span> <span class="special">&lt;&gt;</span>
    <span class="keyword">struct</span> <span class="identifier">begin_container</span><span class="special">&lt;</span><span class="identifier">client</span><span class="special">::</span><span class="identifier">embedded_container</span> <span class="keyword">const</span><span class="special">&gt;</span>
    <span class="special">{</span>
        <span class="keyword">static</span> <span class="identifier">client</span><span class="special">::</span><span class="identifier">embedded_container</span><span class="special">::</span><span class="identifier">iterator</span>
        <span class="identifier">call</span><span class="special">(</span><span class="identifier">client</span><span class="special">::</span><span class="identifier">embedded_container</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">d</span><span class="special">)</span>
        <span class="special">{</span>
            <span class="keyword">return</span> <span class="identifier">d</span><span class="special">.</span><span class="identifier">data</span><span class="special">.</span><span class="identifier">begin</span><span class="special">();</span>
        <span class="special">}</span>
    <span class="special">};</span>

    <span class="keyword">template</span> <span class="special">&lt;&gt;</span>
    <span class="keyword">struct</span> <span class="identifier">end_container</span><span class="special">&lt;</span><span class="identifier">client</span><span class="special">::</span><span class="identifier">embedded_container</span> <span class="keyword">const</span><span class="special">&gt;</span>
    <span class="special">{</span>
        <span class="keyword">static</span> <span class="identifier">client</span><span class="special">::</span><span class="identifier">embedded_container</span><span class="special">::</span><span class="identifier">iterator</span>
        <span class="identifier">call</span><span class="special">(</span><span class="identifier">client</span><span class="special">::</span><span class="identifier">embedded_container</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">d</span><span class="special">)</span>
        <span class="special">{</span>
            <span class="keyword">return</span> <span class="identifier">d</span><span class="special">.</span><span class="identifier">data</span><span class="special">.</span><span class="identifier">end</span><span class="special">();</span>
        <span class="special">}</span>
    <span class="special">};</span>
<span class="special">}}}</span>
</pre>
<p>
          </p>
<p>
            The last code snippet shows an example using an instance of the data
            structure <code class="computeroutput"><span class="identifier">client</span><span class="special">::</span><span class="identifier">embedded_container</span></code> to generate output
            from a <a class="link" href="../../../karma/reference/operator/list.html" title="List Generator (a % b)">List (<code class="computeroutput"><span class="special">%</span></code>)</a> generator:
          </p>
<p>
</p>
<pre class="programlisting"><span class="identifier">client</span><span class="special">::</span><span class="identifier">embedded_container</span> <span class="identifier">d1</span><span class="special">;</span>    <span class="comment">// create some test data</span>
<span class="identifier">d1</span><span class="special">.</span><span class="identifier">data</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">1</span><span class="special">);</span>
<span class="identifier">d1</span><span class="special">.</span><span class="identifier">data</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">2</span><span class="special">);</span>
<span class="identifier">d1</span><span class="special">.</span><span class="identifier">data</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">3</span><span class="special">);</span>

<span class="comment">// use the instance of an 'client::embedded_container' instead of a </span>
<span class="comment">// STL vector</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">karma</span><span class="special">::</span><span class="identifier">format</span><span class="special">(</span><span class="identifier">karma</span><span class="special">::</span><span class="identifier">int_</span> <span class="special">%</span> <span class="string">", "</span><span class="special">,</span> <span class="identifier">d1</span><span class="special">)</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>   <span class="comment">// prints: '1, 2, 3'</span>
</pre>
<p>
          </p>
<p>
            As you can see, the specializations for the customization points as defined
            above enable the seamless integration of the custom data structure without
            having to modify the output format or the generator itself.
          </p>
<p>
            For other examples of how to use the customization point <code class="computeroutput"><span class="identifier">container_iterator</span></code> please see here:
            <a class="link" href="next_iterator.html#spirit.advanced.customize.iterate.next_iterator.example">use_as_container</a>
            and <a class="link" href="deref_iterator.html#spirit.advanced.customize.iterate.deref_iterator.example">counter_example</a>.
          </p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
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